Small engines, particularly, two-stroke engines have been widely used as power sources in small working machines such as cutters, chainsaws, and bush cutters. The two-stroke engines are small and light and can obtain high power output. Therefore, the two-stroke engines can work for a long time by fuel feeding. As one of methods of improving the startability of those engines, there is known a method of opening a throttle valve of a carburetor from an almost fully closed position (hereinafter, referred to as an idle position) by a predetermined amount, thereby increasing an amount of intake air during starting.
In a case of using this method, for example, if the throttle valve is fully opened for starting, the startability of a corresponding engine is improved, but immediately after the starting, the engine speed suddenly increases. Thus, a centrifugal clutch may be engaged such that a front tool such as a rotary blade rotates. In order to prevent this phenomenon, it may be considered to start the engine by slightly opening the throttle valve. However, in this case, since a throttle opening is low, the startability may be reduced. For this reason, as one of methods of preventing revolutions of an edge tool, a brake mechanism for forcibly stopping revolutions of the edge tool during engine starting is provided to, for example, a chainsaw, such that, even if the engine speed increases during the starting, a brake acts to prevent revolutions of the edge tool. However, when the brake is operated, a centrifugal clutch and a clutch housing slide on each other. If this state continues for a long time, the centrifugal clutch generates heat, which causes the clutch housing to wear.
As a technology for controlling the speed of an engine to a predetermined value or less, PTL 1 discloses a technology which, if the speed of an engine is a predetermined speed or more, delays the timing of ignition such that the speed of the engine is maintained at a predetermined value (corresponding to, for example, a bottom dead center), whereby the speed of the engine is controlled.